The off-gassing of ammonia from hardware and metabolic sources presents a unique challenge to trace contaminant control system design, driving process flowrates to meet crewed air quality requirements. Accurately simulating representative trace contaminant cabin loads during ground testing is necessary to validate component design as well as understand potential contaminant propagation across life-support system process interface boundaries. This effort is complicated by the observed temporal concentration instability of gaseous ammonia in ground test chambers. To this end, ammonia concentration decay rates were characterized under controlled environmental conditions to better understand underlying phenomena and quantify incidental mass losses. The suspected chemical interaction between ammonia and trace acetaldehyde was investigated and its effect on species quantification was examined by both gas chromatography-mass spectrometry and Fourier-transform infrared spectroscopy. Recommendations for ground test procedures were made in order to best compensate for undesirable ammonia mass losses and mitigate test artifacts.